- Time:Jan 06, 2023
At present, ferrosilicon nitride is mainly used in carbon refractories such as blast furnace outlet gun clay and iron outlet ditch. Since Fe-Si3N4 has the characteristics of small coefficient of thermal expansion, good thermal shock resistance and not easy to be penetrated by slag, it is also used in synthetic composites, magnesium castables, non-burning chrome-free refractories, etc.
1、Application in refractories of Al2O3-SiC-C system
(1) Application in Al2O3-SiC-C gunite
Tests and industrial applications show that: ferrosilicon nitride can improve not only the physical properties and high-temperature strength of gun clay, but also the opening performance and erosion and scouring resistance of gun clay.
The improvement of application performance has a good effect. In recent years, the national key large iron and steel enterprises above 2000m3 blast furnace plugging iron mouth gun clay basically use ferrosilicon nitride. The gun clay with the addition of ferrosilicon nitride has well met the needs of large blast furnaces, so that the number of blast furnace iron discharge is generally reduced from 18 times to 12 times, and the lowest is reduced to 6 times. The consumption of gun clay is reduced from 1.2kg to 0.5kg per ton of iron.
However, after the addition of ferrosilicon nitride in the gun clay reaches a certain amount, the comprehensive performance of the gun clay is not significantly improved, therefore, the amount of ferrosilicon nitride added should be controlled. It is considered that the best overall performance of the gun clay is achieved when the addition of ferrosilicon nitride is controlled at 10%-20% (w).
A number of studies have been reported on the mechanism of action of ferrosilicon nitride in blast furnace gun clay. In the literature, the traits of ferrosilicon nitride in the gun clay material for the blast furnace outlet were studied. The results found that: at 1250 ℃ began to release team; 1300 ℃ and above, iron often silicification; 1400 ~ 1500 ℃ when the reaction is intense, releasing a large amount of gas, the matrix generated SiC and AlN. analysis that the reaction of ferrosilicon nitride in the gun clay occurred as follows.
9Fe+Si3N4→3Fe3Si+2N2 (1)
3Fe+Si3N4+2C→Fe3Si+2SiC+2N2 (2)
9Fe+Si3N4+Al2O3+3C→2AlN+3Fe3Si+3CO+N2 (3)
It can be seen that the addition of ferrosilicon nitride in the gun clay generates SiC and AlN in the matrix at high temperature, which enhances the matrix and generates a large amount of gas at the same time, which can increase the porosity of the gun clay, improve the opening performance and permeability of the gun clay, and the gas generated can reduce the friction at the contact interface with the iron and prevent slag erosion.
The transformation of silicon nitride to silicon carbide mainly occurs in the iron-carbon nitride system at high temperature, and Fe has an obvious promoting effect on the transformation of Si3N4 to SiC, which is due to the formation of SiC-C complex phase material and strengthens the strength and slag erosion resistance of blast furnace gunite, and the use performance is greatly improved. The reaction of Si3N4 with metal Fe at high temperature generates Fe3Si to increase the amount of liquid phase, which not only promotes sintering, but also promotes the transformation of α-Si3N4 to β-Si3N4 and the formation of long columnar grains; in addition, Si3N4 reacts with C to generate SiC, and a large amount of Si3N4 and SiC cross each other to form a network structure, which improves the high-temperature strength of gunite. However, some people think that above 1300℃, ferrosilicon nitride does not necessarily occur ferrosiliconization, and it is believed that ferrosilicon nitride first decomposes into silicon nitride and Fe, and Fe is easily oxidized to form the oxide solid solution of ferrosilicon, while the decomposed silicon nitride may also be oxidized to generate nitrogen oxides and produce N2, which can avoid the oxidation of carbon and also promote the generation of tiny pores during the sintering process, which is conducive to improving the permeability performance of gun clay and opening performance.
(2) Application in Al2O3-SiC-C textured iron channel material
The addition of a small amount of Fe-Si3N4 to Al2O3-SiC-C textured iron trench material can improve the oxidation resistance of the material and increase the high temperature strength of the material, thus greatly improving the iron throughput of the blast furnace iron-out trench. It is found that ferrosilicon nitride can significantly improve the oxidation resistance of Al2O3-SiC-C iron exit trench castables, and the oxidation resistance increases with the increase of ferrosilicon nitride addition. The antioxidation mechanism is as follows: under the high temperature oxidizing atmosphere, the Si3N4 in the surface silicon iron nitride oxidizes first to form SiO2, which constitutes the main body of the oxide layer; with the oxidation of the iron phase material, the iron oxide formed not only lowers the melting point of the oxide layer, but also lowers the viscosity of the melt, enhances the wettability and fluidity of the melt on the material surface, forms the oxide layer covering the material surface and prevents the oxidation of carbon, which makes It has better oxidation resistance than pure Si3N4. However, the addition of ferrosilicon nitride will increase the water content of the castables and reduce the performance index at room temperature, so the addition of ferrosilicon nitride should be controlled to ensure sufficient construction performance and demoulding strength.
(3) Application in Al2O3-SiC-C bricks
The addition of ferrosilicon nitride to Al2O3-SiC-C bricks for torpedo cars improved the high-temperature flexural strength because the addition of ferrosilicon nitride generated S2N2O at high temperatures, and the high-temperature flexural strength increased with the addition of more ferrosilicon nitride and more Si2N2O.
2、Fe-Si3N4-SiC composite
Si3N4-SiC materials have good physicochemical properties and high temperature performance, and are widely used in high temperature fields such as blast furnaces and aluminum electrolytic cells with good results. Compared with pure silicon nitride, ferrosilicon nitride has better sinterability and can be used as a high-temperature bonding phase. If the mass fraction of 90% and 10% of the industrial SiC and ferrosilicon powder as raw materials, plus 2% (w) of the yellow dextrin, 1380 ℃ 5h nitride firing to prepare Fe-Si3N4 bonded SiC composite, the resulting phase in addition to coincidence for, SiO2, but also contains a small amount of ferrosilicon (FeSi) and monomeric Fe. with a mass fraction of 12% and 88% of the FeSi powder The Fe-Si3N4-SiC composites were successfully prepared by direct nitriding reaction sintering with SiC, α-Si3N4, β-Si3N4 and Fe3Si as main raw materials, and all the Fe-Si intermetallic compounds were in the shape of spheres with diameter less than 10 μm, and the uniformly distributed Fe-Si intermetallic compounds could be used as metal plastic phases. The synthesized Fe-Si3N4-SiC products have better room temperature compressive strength and high temperature flexural strength than Si3N4-SiC materials. Fe-Si3N4-SiC composites contain not only high temperature reinforcing phases SiC and silicon nitride, but also metal plastic phases (Fe, FeSi or Fe3Si), which can improve the thermal shock resistance of the materials, and the materials are expected to have good applications in high temperature fields Prospects.
3、Application in other refractory materials
Ferrosilicon nitride contains silicon nitride and Fe phases, which has a series of excellent properties such as good high temperature performance, low thermal expansion coefficient, good thermal shock resistance and non-permeation by slag, and has also been used in other refractory materials. The University of Science and Technology Beijing used ferrosilicon nitride containing high-temperature enhanced phase silicon nitride and metallic plasticity phase Fe, corundum and spinel as raw materials, and added ferrosilicon carbide in the form of fine powder to prepare a low-cost chromium-free non-burning refractory with good resistance to oxidation and erosion according to the theory of transition plasticity. The refractory has excellent physical properties, good oxidation resistance and steel erosion resistance, and can be used instead of magnesium-chromium bricks for RH refining furnace. The introduction of certain amount of ferrosilicon nitride into magnesia castables improves the strength of magnesia castables after medium and high temperature treatment as well as the thermal flexural strength, because ferrosilicon nitride can be partially oxidized to SiO2 during the heating process, and then form fibrous magnesia olivine, which increases the strength; the iron phase material can solidify with magnesia and promote sintering. The high alumina castables with high thermal shock and good erosion resistance were prepared by introducing ferrosilicon nitride into the high alumina castables, expecting to replace the high alumina bricks used for the parts in contact with aluminum liquid (which require high chemical stability and good thermal shock resistance). It was found that the addition of ferrosilicon nitride reduced the apparent porosity and increased bulk density and strength of the material after drying and firing, and the erosion of the specimen by the slag was reduced, although the penetration of the slag into the specimen increased.
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